Slant plate type compressors such as wobble plate type compressors which reciprocate pistons by converting the rotational motion of a cam rotor into nutational motion of a wobble plate are well known in the art. Such a variable displacement wobble plate compressor is disclosed in Japanese Patent Application Publication No. 58-158,382. Changing the inclined angle of the wobble plate changes the stroke of the pistons and therefore changes the displacement volume of the cylinders.
Referring to FIG. 1, the construction of a conventional wobble plate type compressor is shown. Wobble plate type compressor 1 includes front end plate 2, cylinder casing 3 having cylinder block 31, valve plate 4 and cylinder head 5. Front end plate 2 is fixed on one end of cylinder casing 3 by securing bolts (not shown). Axial hole 21, which is formed through the center of front end plate 2, receives drive shaft 7. Radial bearing 8 is disposed in axial hole 21 to rotatably support drive shaft 7. Annular sleeve portion 22 projects from front end plate 2 and surrounds drive shaft 7, thereby defining a seal cavity. Cylinder casing 3 is provided with cylinder block 31 and crank chamber 32. Cylinder block 31 has a plurality of equiangularly spaced cylinders 33 formed therein.
Cam rotor 9 is fixed on drive shaft 7 by pin 103. Thrust needle bearing 10 is disposed between the inner wall surface of front end plate 2 and the adjacent axial end surface of cam rotor 9. Arm portion 91 of cam rotor 9 extends in a direction toward cylinder block 31. Elongated hole or slot 92 is formed on arm portion 91. Inclined plate 11, provided with flange portion 111, arm portion 112 and cylindrical portion 113, is disposed around drive shaft 7. Arm portion 112 is formed on the outer surface of flange portion 111 of inclined plate 11 and faces arm portion 91 of cam rotor 9. A hole (not shown) which is formed in arm portion 112, is aligned with elongated hole or slot 92. Guide pin 12 is fixedly inserted in the hole so that an end portion of guide pin 12 is slidably movable within elongated hole 92. Ring shaped wobble plate 13 is mounted on the outer surface of cylindrical portion 113 of inclined plate 11 through radial bearing 14 and is prevented from axial movement by flange portion 111 and snap ring 15 which is disposed on cylindrical portion 113. Wobble plate 13 is also prevented from rotating by guide plate 25 which extends within crank chamber 32. Thrust needle bearing 16 is disposed in a gap between flange portion 111 and wobble plate 13. The outer end of drive shaft 7 is rotatably supported through radial bearing 17 in the central bore 34 of cylinder block 31. One end of piston rod 18 is rotatably connected to receiving surface 131 of wobble plate 13. The other end of piston rod 18 is rotatably connected to piston 19 which is slidably fitted within cylinder 33.
Suction ports 41 and discharge ports 42 are formed through valve plate 4. A suction reed valve (not shown) and a discharge reed valve (not shown) are oppositely disposed on valve plate 4. Cylinder head 5 is connected to cylinder casing 3 through gaskets (not shown) and valve plate 4. Partition wall 51 extends axially from the inner surface of cylinder head 5 and divides the interior of cylinder head 5 into annular suction chamber 52 and discharge chamber 53. Annular suction chamber 52 is connected to the external fluid circuit through fluid inlet port 54 formed in cylinder head 5. Discharge chamber 53 is connected to the external fluid circuit through fluid outlet port 55 formed in cylinder head 5.
Crank chamber 32 of cylinder casing 3 and suction chamber 52 of cylinder head 5 are connected to one another through bypass conduit 311. Bypass conduit 311 permits control of the pressure in crank chamber 32 to control the angle of inclined plate 11 and wobble plate 13. Conduit 311, formed within cylinder block 31, provides communication between crank chamber 32 of cylinder casing 3 with suction chamber 52 of cylinder head 5. Conduit 311 includes passage 311a, and hollow portion 311b having control valve 20 therein. Control valve 20 controls the opening and closing of conduit 311 in response to the difference between the gas pressure in crank chamber 32 and that in suction chamber 52. Thus, conduit 311 introduces the fluid gas from crank chamber 32 to suction chamber 52 in response to operation of control valve 20. Control valve 20 includes bellows 20a, under vacuum, and needle valve 20b. One end of bellows 20a is mounted on a projection formed on the inner wall surface of hollow portion 311b. Needle valve 20b is fixed on the other end of bellows 20a. When the pressure in crank chamber 32 is greater than the operating pressure point of bellows 20a, bellows 20a contracts with needle valve 20b moving therewith, thereby opening hole 43 in valve plate 4. Accordingly, the high pressure gas in crank chamber 32 flows into suction chamber 52, thereby reducing the pressure in crank chamber 32.
In the above construction of a wobble plate type compressor with a variable displacement mechanism, it is necessary to form bypass conduit 311 in cylinder block 31 to dispose control valve 20 therein. Furthermore, since hollow portion 311b is formed outside of the circumference of the plurality of cylinders 33, the outer surface of cylinder casing 3 projects in the radial direction as shown in FIG. 2. Alternatively, if hollow portion 311b is formed on the circumference of cylinders 33 to prevent cylinder casing 3 from so projecting, respective cylinders 33 could not be disposed at regular intervals, e.g., equiangularly spaced, thereby causing pulsation of the gas pressure. Furthermore, if control valve 20 is disposed within a cylinder head, the volume of the suction chamber and discharge chamber is reduced. This configuration also causes increased pulsation of the gas pressure.
The angle of inclination of inclined plate 11 and wobble plate 13 is dependent on the fluid pressure in crank chamber 32. If the communication between crank chamber 32 and suction chamber 52 is prevented by closing control valve 20, fluid pressure in crank chamber 32 gradually increases. The high fluid pressure in crank chamber 32 acts on the rear surface of pistons 19 thereby reducing the angle of inclination of inclined plate 11 and wobble plate 13. The capacity of the compressor is also reduced. On the other hand, if crank chamber 32 and suction chamber 52 are in communication with each other, as when control valve 20 is open, fluid pressure in crank chamber 32 is reduced thereby affecting the increase in the angle of inclination of inclined plate 11 and wobble plate 13. The capacity of the compressor is increased as well.